1. Field of the Invention
The present invention relates to a miniature printer used in a cash register or the like. Particularly the present invention relates to a device for controlling the head pressure in a miniature printer, in which a pair of hinge parts with an elongate shaft retaining slot in each of them are formed on the bottom of a head frame so as for a printer head to be closely contacted to the surface of a platen roller. Elastic members are fixed to the head frame, and a supporting bracket is installed in rear of the head frame across the elastic members so as to be pivoted together with the head frame, so that a stable running of the printer paper is ensured, and the printing state is made clear.
2. Description of the Prior Art
In the generally known miniature printers used in a cash register or the like, as shown in FIG. 1, a printer head 10 is integrally formed with a head frame 12, and at the rear of the head frame 12, there is installed a supporting bracket 16 to be elastically supported by springs, so that the head frame 12 and the supporting bracket 16 would be elastically supported. A pair of hinge parts 18 are formed on the bottom of the head frame 12 and the supporting bracket 16.
Further, a shaft 22 is formed upon a base plate 20, and a locking piece 28 is pivotally installed on the rear face of the supporting bracket 16. When the lower end of the locking piece 28 contacts a projected step 24, the printer head 10 contacts a platen roller 26.
In the above described printer, the head frame 12 together with the printer head 10 is pivoted forward by a certain angle to be contacted to the platen roller 26 (the printing paper passes by the roller 26), thereby carrying out the printing. In this case, springs 14 are installed to the rear face of the head frame 12, and thus the supporting bracket 16 pivots together with the head frame 12. Thus if the locking piece 28 is turned downward, the supporting bracket 16 pivots around the shaft 22. Under this condition, the head frame 12 together with the printer head 10 pivots forward to make the printer head 10 contact the platen roller 26, and therefore, a printing operation is carried out on the paper which passes through the platen roller 26.
However, in the above described printer, the head frame 12 is pivoted in accordance with the pivoting of the locking piece 28. Therefore, when a contacting force acts on the platen roller 26, a part of the printer head 10 closely contacts with the platen roller 26 owing to the incoming paper, while gaps remain at either of the end portions of the printer head 10. Due to these gaps between the printer head 10 and the platen roller 26, a clear printing cannot be realized.
A printer related to this technique is disclosed in Japanese Patent Application Laid-open No. Hei-7-25084.
This printer is illustrated in FIG. 2. As shown in this drawing, springs 52 are secured to the rear face of a head frame 50, and a printer head 54 is supported by the springs 52. A platen rubber member 64 is supported by a shaft 58 which is secured on a base frame 56. Inside the platen rubber member 64, there are installed a main platen supporting member 62 and an auxiliary platen supporting member 60, so that the platen rubber member 64 can be closely contacted to the shaft 58. Further, the platen supporting members 60 and 62 respectively have contacting parts 66' and 66. A printing paper roll 68 is disposed on a side of the base frame 56.
In the above described printer, when the printer head 54, which is elastically supported by the springs 52 of the head frame 50, is contacted to the platen rubber member 64, the platen rubber member 64 contacts both of the contacting parts 66' and 66, and therefore, a stable position is maintained all the time. The contacting parts 66 and 66' which are formed respectively within the platen supporting members 60 and 62 contact with the shaft 58 so as to be rotated together with the shaft 58. Accordingly the printer head 54 stably contacts with the platen rubber member 64, thereby carrying out a printing on the paper of the paper roll 68.
However, the printer head 54 which closely contacts with the platen rubber member 64 always contacts with a side of the base frame 56. Therefore, if the platen supporting members 60 and 62 are damaged, then a part of the printer head 54 contacts with the platen rubber member 64, while a gap is formed between the other ends of the printer head 54 and the platen rubber member 64. At this situation, the adjustment of the gap is very difficult, and therefore, the printing quality is aggravated, or the paper is ejected in a skew posture, or the paper may be jammed.